The present invention relates to an apparatus for manufacturing a flat multi-conductor cable. More particularly, the invention relates to an improvement in an apparatus for manufacturing a flat multi-conductor cable having laterally aligned twisted and straight portions at predetermined and periodic intervals.
A conventional flat multi-conductor cable having laterally aligned alternating twisted and straight portions at predetermined and periodic intervals was disclosed, for example, in U.S. Pat. No. 4,096,006 entitled "METHOD AND APPARATUS FOR MAKING TWISTED PAIR MULTI-CONDUCTOR RIBBON CABLE WITH INTERMITTENT STRAIGHT SECTIONS" and issued to Patrick Joseph Paquin on June 20, 1978. The flat multi-conductor cable disclsed in this patent is constructed to have a plurality of twisted insulated conductor pairs in combination with intermittent straight sections laminated therein at precise lateral spacings. A plurality of conductor pairs are maintained at lateral spacings by alternately laminating the twisted portions of the conductors and the straight portions of the conductors, between upper and lower plastic films with both the upper and lower plastic films being subsequently heat welded under pressure to each other on either side of the conductors. Since such a conventional flat multi-conductor cable maintains the precise lateral spacings between the conductor pairs by heat welding under pressure between upper and lower plastic films laminated on either side of the conductors pairs, it is relatively difficult to maintain the flatness of the flat multi-conductor cable in the lateral spacings between the conductor pairs. This inconveniently introduces an uncertainty to the arrangement of connectors for the flat multi-conductor cable. Further, the twisted portions of the conductor pairs of the flat multi-conductor cable have reduced flexibility due to the presence of the plastic films laminated on both sides of the conductor pairs which causes considerable inconvenience when being used in a limited space.
It has been proposed to eliminate this inconvenience by having a flat twisted cable which does not employ such lamination of plastic films but which only heat welds the insulative coatings of single-conductors in the straight portion to each other, thereby providing excellent flatness of the straight portion while keeping the twisted portion highly flexible.
Such a conventional flat twisted cable is manufactured by passing a plurality of single-conductor pairs through a twister formed of tubular or straw dies with the nozzle outlets of the straw dies being disposed in a common horizontal plane while suitably laterally converging the single-conductor pairs, alternately twisting the conductor pairs clockwise and counterclockwise with non-twisted portions of the single-conductor pairs coated between the twisted portions, temporarily terminating the forward travel of the conductor pairs when the straight portion of the conductor pairs reaches a heat welding section disposed at a predetermined position and heat-welding the conductor pairs of the straight portions of the flat cable therebetween. Since the manufacture of such a conventional flat twisted cable is intermittent, the manufacturing speed is low and problems arise with respect to the uniformity of the products. Inasmuch as the apparatus for manufacturing the conventional cable operates intermittently, the maintenance of the apparatus is relatively difficult. In addition, the apparatus is relatively complicated and excessively large when the whole operation of the apparatus is to be automated.
Moreover, in a conventional apparatus for manufacturing a flat cable, in order to overcome the problem of converging single-conductor pairs toward each other during a period from the step of deriving the single-conductor pairs from the bobbins to the step of heat welding and the problem of effectively heat welding the straight portions of the conductor pairs in the step of heat welding, the conductor pairs of the cable are normally roughly converged by using springs. Subsequently the conductor pairs thus roughly converged are supported by a double fork device. Thereafter the pairs are converged further toward each other in a predetermined width and the conductor pairs thus further converged are eventually converged even further by a single-fork device. Since it is necessary to provide sufficient space so as to converge the conductor pairs in such a multiple step operation, such a conventional apparatus inevitably must increase in size.